Pakistan’s embattled ISI intelligence service has retained U.S. lawyers to block a lawsuit alleging that its current and former directors helped one of the world’s most dangerous terrorist groups conduct the Nov. 2008 attack in Mumbai, India, killing 164 people, including six Americans.

The lawsuit, filed late last year in U.S. federal court in New York by American family members of the victims and one survivor of Mumbai, is based in large part on evidence developed by the FBI linking the ISI to the operatives of the Lashkar e Taiba terror group who are charged with conducting the operation.

The lawsuit charges that the ISI provided “critical planning, material support, control and coordination” of the Mumbai attacks under the leadership of its director general, Ahmed Shuja Pasha, and his predecessor, Nadeem Taj. This allegedly included providing funding to David Coleman Headley, a Pakistani American who has pleaded guilty in federal court to conducting surveillance for the Mumbai attacks under the direction of an ISI case officer, whom he identified only as “Major Iqbal.”

But U.S. lawyers for the ISI are now moving to quash the lawsuit, arguing that if the case proceeds, it “will fuel violence and extremism” that will threaten the Pakistani government and pour “gasoline on the fire” of relations between Pakistan and India.

'An intrusion on its sovereignty'
The Pakistani government “regards any assertion of jurisdiction over its high officials” by a U.S. court “as an intrusion on its sovereignty, in violation of international law,” according to a brief filed late last week by two U.S. lawyers, Kevin Walsh and Allen C. Wasserman, on behalf of the ISI.

The brief also argues that Pakistan is a strong “wartime ally of the United States” in the fight against al-Qaida and the Taliban in Afghanistan and that the lawsuit would damage that alliance.

The two lawyers are with the Dallas based firm of Locke Lord Bissell & Liddell, whose lobbying arm, Locke Lord Strategies, represents the Pakistani government in Washington. The firm reportedly has collected over $2 million in fees since it signed a contract with the Pakistani government in 2008.

Among the firm’s partners who are registered as lobbyists for the Pakistanis are two former top aides to President George W. Bush — Harriett Miers, a former White House counsel, and Roy Coffee, one of his chief legislative aides when he was governor of Texas. The chief of the firm’s Pakistan lobbying account is Mark Siegel, a former executive director of the Democratic National Committee and political aide in the Carter White House.

Contacted by NBC News, Walsh, the lead lawyer in the case, declined to comment beyond what was filed in his court brief, other than to note that the Pakistani government has denied the allegations that an ISI officer assisted in the Mumbai attacks.

'I'm a lawyer, not a lobbyist'
“I’m a lawyer, not a lobbyist,” he replied when asked if he was representing the ISI as part of his firm’s lobbying contract with Pakistan.

The court filing comes amid mounting tensions between the U.S. government and Pakistan over suspicions that some elements of the ISI continue to maintain ties to various terrorist groups, including Lashkar e Taiba, that are aligned with al-Qaida.

Those suspicions have been fueled by the discovery that Osama bin Laden lived unmolested for years in a compound in Abbottabad, close to Pakistan’s premier military academy.

“It’s incomprehensible for me to believe that no one around there knew,” U.S. Sen. Diane Feinstein, chairwoman of the Senate Intelligence Committee, told reporters on Tuesday. “To enable him to live in Pakistan in a military community for six years, I just don’t believe it was done without some form of complicity.”

Feinstein also said the relationship between the U.S. and Pakistan is becoming “increasingly problematic” in light of the bin Laden discovery as well as the ISI’s alleged support for the Haqqani network, a militant group that has been attacking U.S. troops in Afghanistan.

Pakistan also has failed to turn over accused co-conspirators linked to the Mumbai attacks to the U.S. and India. One of those is “Major Iqbal,” who has been charged with assisting those attacks in an indictment unsealed by U.S. attorney Patrick Fitzgerald’s office late last month. Headley is expected to testify as the star witness in the trial that begins later this month of a Chicago businessman, Tahawwur Hussain Rani, accused of providing him with cover while he conducted surveillance for the attack.

James P. Kreindler, the lawyer who filed the suit against ISI, said recent developments, including the indictment in Chicago and the aftermath of the bin Laden raid, make his case “many times stronger.” As a result of those developments, he said, “the Pakistanis have no credibility and they’re playing a double game.”